Connecting extruded aluminium?

I hope this question was not asked too often. I nearly got killed as I looked for alternatives on connecting extruded aluminium profiles. One connection is doubled of the cost for the profile so I am looking for cheap alternatives.
What did you use to connect your profiles?

If you're talking about T-slot extrusions like 8020 or Misumi or any similar types, they are easily joined with only a screw and a washer. You'll need a tap and a drill.

Tap the end hole- the holes are sized for standard taps- just find out which size is the right one by reviewing the manufacturer's literature. Next get some button head cap screws and washers that fit inside the slots. Finally, drill a tool access hole and use it to tighten the screw.

That is indeed a good idea. There is a online-shop with a branch here in Germany they cut the Aluminium extrudes for free and it only costs less than 3€ per meter.
The simplest idea you will not get. That is pretty good. A little bit work, but good. The only problem are maybe the screws, but the shop offers cheap one which cuts the threads by themselves. I think they could work and I think I saw this mounting there on a picture. Shame on me.

They're like 1€ per piece, so not this cheap if buying ... but I've got several frames, sets and other bits'n'bytes through my developments (or from the scrapery) over the years for free, so not counting per money

Do you have a working printer? You can print your own corners. You can see how mine looks HERE. It requires a little thinking when designing your corners because they have to be really big to get a decent strength and rigidity. You can't just copy a steel bracket and print that.

I see a lot of variation in how people use this stuff. Lars likes oversized plastic corners... did you ever try screwing the frame pieces directly to each other?

This thing screams solid-as-a-rock, but look at all the little corner pieces he used and the hundreds of screws required to hold it all together. Can those corners possibly add any rigidity beyond simply screwing the frame pieces together (which he doesn't appear to be doing)?

The whole point of using these extrusions is their rigidity and ease of construction. If you're using t-slot extrusions, you don't need corners. The stuff is designed to be easy to bolt together and to attach other things to it. What will be more rigid, bolting aluminum directly to aluminum or putting a piece of plastic between pieces of aluminum?

Besides screwing the extrusions to each other, you can easily attach other parts to the rails using standard carriage bolts. The squared part of the head fits into the slot in the extrusion which prevents the bolt from rotating when you tighten down its nut.

The 8020 material I used is 1.5" square and is designed to work with 5/16"-18 screws and carriage bolts. The center hole is sized for a 5/16-18 tap and the slot width fits 5/16" carriage bolts. Other size extrusions are sized for other hardware- you just have to check the specs to figure out which hardware works, then invest a few $ in a tap and a hand drill to make the tool access holes.

This is exactly how the stuff is designed to be used. It is the reason why the slot is the size it is and the reason why the center hole is the size it is.

QuoteLarsK
Do you have a working printer? You can print your own corners. You can see how mine looks HERE. It requires a little thinking when designing your corners because they have to be really big to get a decent strength and rigidity. You can't just copy a steel bracket and print that.

Hello Lars. I still could use option 1 with the simple screw. How big is your heated bed? I am also looking for the connection of it.

Quotethe_digital_dentist
I see a lot of variation in how people use this stuff. Lars likes oversized plastic corners... did you ever try screwing the frame pieces directly to each other?

Now I do something what I do not like to do, I am sorry it is too early in the morning. Normally I would have posted only one answer.

I have not started the design yet, but I plan do start within the next 2 hours or so. As I lnked above the shop where I will order the extrudes directly offers connection screws which also cut the thread by themselves. They also cut the extrudes so you are sure that they are angled. This seems to be indeed the best option. I then could print some caps and maybe adding some adhesives feet. Okay this would end in some small drilling for the allen key but this would be okay. It is much cheaper then the connectors.

I use a screwed in connection (through the profile holes) on the upper parts of my newest printer. It is a fine solution and more space economic which is why I used it. To obtain a strong connection it requires perfect cuts of the alu profile because the stability is dependent on full face contact with the alu. I am not able to get that with my hand-saw but if you (Treito) can get the company to cut then I think that would be worth trying out.

I have been looking to buy a circular table saw for my cuttings for a while, but with the very few cuts it is hard to defend the cost.

The experiences I have made with the end-screws makes me less sure that it can work as a stand alone solution on a bigger printer with just 2020 profiles. Even when it seems tight it does allow some rotation in the joint so that the entire structure can flex when no cross bracing is used. That could just be my bad cuts though. At the end of the day, as long as no one gets some solid measurements it becomes really hard to determine.

The good news is that you can do the end-screws, and if that does not work for you, you can print some big corners or buy the metal ones.

Thanks for the answer, bu now for the third time:
The company cuts the extrudes to length and they offer the screws designed for this connection even self-cutting.
Sorry, I wrote this too often in this thread.

QuoteTreito
Thanks for the answer, bu now for the third time:
The company cuts the extrudes to length and they offer the screws designed for this connection even self-cutting.
Sorry, I wrote this too often in this thread.

Uhm... Okay...

Maybe I was unclear when I wrote that:

Quote"... you (Treito) can get the company to cut then I think that would be worth trying out."

I meant to say that if you can get them to cut it (use that service, etc.) then that would be worth trying out.

1) Seriously, relax. Stop this "desperate" and "nearly killed me" rhetoric. It does not look good in writing.

2) It is not about if it is free of not. It is about if it is the best solution. If you read my reply you will see that I am not so convinced that for 2020 profiles the end screws will be enough for the stability you need. Even with perfect cuts. I do not know this for a fact. But I am seriously doubtful.

3) If you are using the shop you linked before ( Motedis ) then it seems to me they charge 1€ for each M5 cut - I can't see how "self cutting screws" would work - But do enlighten me.

2) Like you said you cut by yourself and the_digital_dentist had success withthis method.

3) First of all self cutting screws have s special thread on how they cut like sheet metal screws. A self-tapping screw. Besides I used an ordinary allen-key (countersunk) screw to cut threads into my extrudes of my Ormerod 2.

He is using 1.5" = 38.1 mm x 38.1 mm profiles. You are thinking about 20 x 20 profiles. Not the same thing.

He is using 5/16" bolts = ~8 mm. You are (as I understand) thinking about 5mm or 6mm - or even some kind of self cutting screw. Not the same thing.

I would still like to see a link to these self-cutting screws that can work in the alu profiles from Motedis. As I read their website they recommend to tap with M5 or M6 and they offer this at 1€ for each hole. Just as they offer to do the individual cuts for you at 0.09€ extra per meter (or for free if you make it sum to 3m pieces).

As I said in my earlier post I think you should go ahead and try it out anyways. If it doesn't work, you can improve on it later as slapping some metal angles on it is pretty easily done.

Ah, that is actually cool. I have always wondered why some profiles did not feature a "normal" hole and instead these "ribs" - Now I know - It is so that it works with self cutting screws. Learning a little everyday.

The corner you are showing is great for this kind of application because they can hold a static load and prevents torsion. Also it is inside the frame, and does not protrude so you can still mount a plastic panel flat on the structure.

It is not good against moments of bending alone because it is only secured with one screw. If you combine this with an end-screw then it will be better. But if you wanna start using brackets to reinforce the structure, then I think this is the best choice:
[www.motedis.com]

Did you review this photo collection (ZIP file) that I posted in the CoreXY forum? When in doubt, look for the printers you think look good, and do like they do. Printers that looks great usually also is.

Your last link is the problem that I have. Of course I can use this, do you pay it for me? Seriously if I would consider spending so much many for the frame I would by a different one. I am aiming to build a printer which is better than an I3 or an Ormerod where the price does not exceed the price for the Ormerod. So the limit is 600€ for the whole printer, but keeping it as cheap as possible.
Of course I looked at your picture. I do not know where I saw them but there are many printers out there where I get really afraid for. Especially the electrical connections...
Damn that is indeed my problem I have to make the frame more complicated than I wanted as I need some guidance somehow for the cable chain.

For the high cost of all those little pieces that some people use to bolster a frame, they could probably just buy larger cross-section extrusions that don't need any bolstering.

In other words, if the extrusion you've chosen needs a lot of bolstering, you've probably chosen the wrong extrusion... unless you chose to use aluminum extrusion for its "professional" look and not its performance...

Edited 1 time(s). Last edit at 12/30/2015 07:07PM by the_digital_dentist.

We had once an mechanical engineer at our company. Who designed everything good but we could not sell it. Why? Because he planned so much security in his designs that we were not able to sell it as it was too expensive.
I did not tell that the extrusions are too weak. I only asked for cheap solutions. Cheap! Like I said there are always possibilities to get a little bit more stability. Why not use a stainless steel frame and welder the connections?
I spoke with one person who is in CNC and that person told me that 20x20 would be enough. Of course there will be always a better way and I said before I use a solution with 20x20 extrusions which costs 200€ I would consider another solution.
But I am looking for a cheap and stable solution and not for a Tesla Model S.

A frame made of welded steel tubing would be cheap and rigid. It would be a little more difficult to attach things to it, but that's the trade off you make to be cheap and rigid. If you have welding equipment and know how to use it, it's a good option.

3) buy 2040 profiles (6.5€ at motedis) this will allow to screw in two screws in each connection

4) try just end screws with 2020

5) buy 4040 and then you can be pretty sure it will work as per dentist description.

I understand your price concern. I don't have any final answers on the most cost efficient solution, I think this, what we are talking about now, is pretty close to the frontier of corexy development/optimization

I have no welding equipment and the welding was some sort of joke, but this would have been the stablest variant. The second problem is that it should be of course some sort of RepRap printer so easily to recreate.

2) Is out of race. It would not make me happy looking at it. Besides that a German computer magazine publisher (Heise) tested closed chambers versus open chambers and they did not notice any differences. Unfortunately it was an internal test only so it was mentioned only with one sentence in an article. I would more prefer a design more like snappy even though it is not a CoreXY and I would always use GT2 belts. But it would be more expensive and more loud than Aluminium extrusions.

4) and 5) Disadvantage: You may twist the extrusion

1) Maybe for smaller areas like the heated bed carriage. At a Facebook group I nearly got killed as they told me as I considered this idea. It would not be precisely enough as no printer prints 90° perfectly and it would be too weak. Even if I print a dice? You could directly print connectors onto it so it should not be weak, should it?

3) I really may consider this even though it would double the price. Using this however I would have to check how to align the extrusions because of the asymmetric profile. Maybe front and back at top and bottom layed down. This profile would give me other advantages which are not revealed yet. I would like to have some special designs and two days ago I had a new and really good idea after I gave up the idea to print the frame.

Even if the plate only costs 5.34€, why is it still so expensive? 1 meter extrusions needs more material and costs only half of the price. Okay it is of course another production process but in my eyes it is not more worth than 3€. I guess the margin of the extrusion is not much and the money comes back with the help of the additional parts needed like inkjet printers.

Edit: That would have been too easily. There are no self tapping screw connectors for the 20x40 I-style profile and the 20x40 B-style profile costs around 9€ per meter.

QuoteTreito
I have no welding equipment and the welding was some sort of joke, but this would have been the stablest variant. The second problem is that it should be of course some sort of RepRap printer so easily to recreate.

Ah, philosophy! Philosophy is like a bag of bricks you carry around everywhere you go. Who are you carrying it for? Why not just set it down?
In your philosophy, what is the definition of "easy" and to whom does it apply? Someone with welding equipment can easily recreate a welded frame, a quadriplegic can't. Are you planning to go into production or building a printer for your own use? How does this philosophical ideal rank among the numerous constraints you're putting on this project? Philosophy and quality are in direct opposition to each other- the more 3D printer reproducible the machine is- i.e the more printed content a printer has- the less likely it is to produce quality parts. Maybe your philosophy can be interpreted in a way that will allow you to proceed. Maybe it's OK if the printer can't reproduce itself but can produce high quality parts for other printer designs. Wouldn't it be better, philosophically speaking, to be able to produce very high quality parts so that the printers made from those parts work well, or is the philosophy only about quantity, not quality?

QuoteTreito2) Is out of race. It would not make me happy looking at it. Besides that a German computer magazine publisher (Heise) tested closed chambers versus open chambers and they did not notice any differences. Unfortunately it was an internal test only so it was mentioned only with one sentence in an article. I would more prefer a design more like snappy even though it is not a CoreXY and I would always use GT2 belts. But it would be more expensive and more loud than Aluminium extrusions.

It doesn't matter what you use to make the frame, if you intend to print with ABS you will need a closed build chamber. The chamber must be a warm 45-50C, or ABS prints will warp and delaminate. That means you should put the electronics outside the build chamber, so unlike most designs where positioning the electronics and cables are an afterthought, you should plan the location in advance and design the frame to include warm and cool zones, and design it for easy access to the electronics for maintenance and repairs.

QuoteTreito4) and 5) Disadvantage: You may twist the extrusion

Yes, a single screw butt joint can allow the frame pieces to rotate unless there is something attached to them that prevents rotation. That is how my printer is built. Once the screws are tightened down it is very difficult to rotate any of the frame pieces. In the two years my original printer was in use the screws never loosened and none of the frame pieces ever rotated. The machine has been in its current form for a year without any rotation. There are no rotational forces applied, so the pieces don't rotate. Look at it this way- there's nothing to prevent a screw and nut from rotating either, yet without tools it is very difficult to get them to rotate. The frame piece receiving the screw is a nut.

QuoteTreito1) Maybe for smaller areas like the heated bed carriage. At a Facebook group I nearly got killed as they told me as I considered this idea. It would not be precisely enough as no printer prints 90° perfectly and it would be too weak. Even if I print a dice? You could directly print connectors onto it so it should not be weak, should it?

I would avoid putting any printed parts anywhere near the bed plate. Printed corners are not as strong, rigid, or reliable as metal to metal attachment, and they don't look very nice, but they may be strong, rigid, and reliable enough. People have successfully built printers with them. Printing corner cubes could work, but how is butting aluminum to a piece of plastic better than butting aluminum to aluminum? I milled the ends of the frame pieces square so the butt joints in my frame needed no shims. Whether you're butting aluminum to aluminum or to plastic, you may have to shim the joint to make it square, depending on how square the aluminum is cut and how square the plastic is printed.

QuoteTreitoEven if the plate only costs 5.34€, why is it still so expensive? 1 meter extrusions needs more material and costs only half of the price. Okay it is of course another production process but in my eyes it is not more worth than 3€. I guess the margin of the extrusion is not much and the money comes back with the help of the additional parts needed like inkjet printers.

Aluminum plate is cheap and so is a drill bit. You can easily make the flat plate connectors with a saw and a hand drill. Then you attach the plates to the frame using carriage bolts. It's a lot of hardware, but it's pretty cheap, and pretty easy. If the screw holes in the plate are slightly oversized, there will be enough slop that you'll easily be able to make the joint square.